The V6 F25 is located on the right hand end (as
looking at front of vehicle) of the transversely mounted C25XE engine. It
can be seen better when the alternator cooling fan + ducting and power
steering fluid reservoir are removed.
Changing the clutch on the F25 is more difficult than other calibra models
due to the pot shaped flywheel. The gearbox housing must be separated away
from the engine bell housing by more than 1" to gain proper access to change
out the clutch assembly.

The F25 is considered a poor choice for the C25XE due to
its lazy, long gearing and heavy flywheel. There is a lot of truth to this
which is why a lightened flywheel and F28 six speed
gearbox (converted to 2WD mode) are a popular V6 modification. This really
transforms the driving characteristics of the V6 and can best be described
as more 'lively'. At the very least, if your V6 clutch has gone consider it
an opportunity to change out the heavy flywheel for a new lighter
aftermarket version. You won't regret it, the engine revs a lot more freely.

The F25 is still an OK gearbox. It is reliable and good for 150,000 +
miles. Once
you get used to the long gearing and learn to rev the V6 hard, it's not so
bad. It's also rated to 250 bhp so easy handles most of the demonstrated
performance mods (cams, large throttle body, etc). Third gear is good for up
to 110 mph so leaving it in third to get you up to 70-80 is the way to do
it; after all, the V6 engine really sings at high revs.

F25 : System
Overview

F25 : Differential

F25 : drive shaft,
main
shaft & return shaft

F25 : clutch release
lever

If you are having problems changing gears on your V6
then consider following some of the procedures described below before you
assume that the clutch is on the way out (try in this order - check/adjust
clutch, check gearbox fluid level, check/adjust gear linkage).
However, there are some clear indicators when then clutch is going. One sign
is a whirring noise which disappears when you lift the clutch pedal up with
your foot.

Before Gearbox Fluid Top Up &
Clutch Adjust .........
When you require access to the top of the gearbox (for clutch adjust and
gearbox fluid fill) you will find it easier to remove the alternator ducting
and mini blower, the PAS reservoir and optionally the battery. The engine relay box
should also be removed if you need to replace the clutch cable. These are all
straightforward to remove and doing so will make some gearbox jobs a lot
easier.

alternator air cooling
system

single bolt retains PAS
bottle

two bolts, a clip & cable
grommet
to remove the engine bay relay box

Gearbox Oil Level Check

Jack up the vehicle and work from
underneath. Remove the F25 gearbox oil level check bolt (torx bolt).
This is situated on the back of the F25 housing. You will need an
extension to reach it. It is above the front axle which will obstruct
access.
With the bolt removed a small amount of transmission fluid should
trickle out. The correct level is to the base of the level check bolt
hole.

view from under
car - rear of gearbox

If you need to top up the gearbox
oil you must do so through the top up bolt hole. This is situated on
top of the F25 gearbox housing and best accessed from above. You will
find it much easier if you first unbolt the power steering fluid
reservoir and move it out of the way. Once you have clear access,
remove the torx bolt and carefully top up the fluid through the bolt
hole. Use a small funnel to avoid spillage. Top up until fluid
dribbles from the level check hole.

If you
want to replace the gearbox oil then use a hand pump and hose tool to
extract the old oil through the fluid level check hose. 1.8 to 1.9 litres of new hydraulic transmission oil will be
required to refill (2 x part no : 90 540 998)
(SAE-80)
On late V6 F25 gearboxes there is a bottom drain bolt which can be
removed to drain the gearbox.

Check the clutch pedal travel range and position to determine the
correct setting of the clutch cable adjuster. The clutch pedal
position will change with
normal clutch wear over time.
Adjusting the clutch cable is part of normal maintenance

The
clutch cable is adjusted at the gearbox end. It's difficult to see the
clutch adjuster from above. It is obscured beneath the power steering
reservoir, just behind and underneath the battery tray. You will
need to reach underneath and feel with your fingers.
The adjuster retains the cable to the clutch release lever. Pull the
cable towards you and push the lever away slightly. The adjuster and
cable should just lift out to the side.
(seeBefore Gearbox Fluid Top Up & Clutch Adjust .......).

It is a good idea to make a note of the original
clutch cable position before you start to make any adjustments. Remove
the clutch cable and retainer from the arm, adjust and replace. Wind
the adjuster in (leaving more thread hanging out of the end) in order
to lift the clutch pedal higher. Let the adjuster out (less thread
showing at the end) to drop the clutch pedal position lower to the
floor.

To
replace the clutch cable you need to detach it from the cable adjuster
at the gearbox end. Next detach the clutch cable from the retaining
bracket behind the clutch pedal from underneath the vehicle. Now feed the
old cable trough the engine bay. Note that the is a rubber grommet
where the cable is routed through the engine bay bulkhead.
NOTE: Late model V6's use a slightly longer clutch cable.
"T" chassis variants and later require the longer clutch cable.

Adjusting the gearstick/gearbox linkage

Step One
Working from underneath the
vehicle, loosen the shift rod clamp bolt

In order to gain better access :
Remove alternator cooling ducts - upper and lower (to alternator
cooling cowling). Remove the bracket for the top flat cooling duct as
it will stick in your arm as you are trying to access the clutch cable
adjuster. Remove the small alternator cooling fan unit.
It is also a good idea to remove the bolt holding the power steering
fluid reservoir and move the reservoir out of the way and also the
battery
(seeBefore Gearbox Fluid Top Up & Clutch Adjust .......).

.

Step
Two
Extract the plug bolt from the adjuster
hole (replace with new one after you have finished). Use a screwdriver
or 4 mm old drill bit and insert into the adjuster hole while
jiggling/rotating anticlockwise with the gear adjuster tube.
Turn it to the left. Eventually the drill bit will engage with the selector hole. This will
hold it.

Step
Three
Inside the car - unclip the
gearstick surround cover and peel back out of the way of the base.
This gives you access to the gearstick linkage. Tilt gearstick until
holes align (see right). Insert something into the holes to lock in
place.

## NOTE :
It is recommended that you use a new plug bolt (90578997) as this seal
at the top of the F25 gearbox is vital. A Vaux technical bulletin was
issued (Exxxxxxxx) describing:
F25 equipped vehicles travelling at high speed will have foaming
transmission oil. The foaming gearbox oil will egress through the
gearshift alignment pin hole; unless the hole is properly sealed and
protected. The original part was modified in 1996 to include an extra
'O' ring on the bolt (90578997).

Reverse gear switch (for reverse light)

Reverse
light switch and connector. Replace by removing connector and
unscrewing from gearbox housing. Use new washer/ring seal and tighten
to 20 Nm torque